how to inject FastAPI bearer instances into Depends

[mxab]

Hi,
I'm currently struggeling on how to get this to work.

I have a third party "factory method" that provides me with a method I can use in FastAPI's Depends resolver

from third_party import auth_factory

@app.get("/foo")
def foo(user = Depends(auth_factory(scope="read", extractor = some_token_extractor ))):
    doSomething()

the oauth_factory produces as callable with fastapi know signature

def user_checker(oauth_header:HTTPAuthorizationCredentials = Security(bearer))
   ...
   return user

My problem now is when I want the some_token_extractor be provided by python-dependency-injector

something like this does not work:

user_detail_extractor = Provide[Container.user_detail_extractor]

@app.get("/with_di")
def with_di(user = Depends(auth_factory(scope="read", extractor = user_detail_extractor ))):

    return {
        "user": user["username"]
    }

class Container(DeclarativeContainer):

    user_detail_extractor = providers.Callable(some_di_extractor, some_config="bla")

I have a full demo setup here
https://github.com/mxab/fastapi-di-depends-issue/tree/main/fastapi_di_depends_issue

but I cannot get this test work:
https://github.com/mxab/fastapi-di-depends-issue/blob/main/tests/test_fastapi_di_depends_issue.py#L27

Does this in general not work or what is it I'm missing

Thanks very much in advance

[rmk135]

Hi @mxab , thanks for providing an example. I'll take a look.

Does this in general not work or what is it I'm missing

Dependency Injector can not introspect arguments of Depends(auth_factory(...)). It expects Depends to contain Provide marker. Something you could try is to make injection directly to the auth_factory here https://github.com/mxab/fastapi-di-depends-issue/blob/main/fastapi_di_depends_issue/third_party.py#L20

[mxab]

I think for now I was able to realise to do the DI part via a class that implments __call__ and using an instance of this in the Depends call.

Thanks!

[mxab]

Hi @rmk135,
I think I'm still facing the problem on how to marry this.
I have a simpler show case now just with FastAPI's Bearers classes

Some container:

class Container(DeclarativeContainer):
    config = providers.Configuration()
    bearer  = providers.Singleton(HTTPBasic, auto_error=config.secured.as_(bool))

The application:

app = FastAPI()

#### working
fixed_bearer = HTTPBasic()
@app.get("/fixed")
def fixed(user: HTTPBasicCredentials = Depends(fixed_bearer)):

    return {"username" : user.username}

#### not working
di_bearer = Provide[Container.bearer]

@app.get("/with_di")
@inject
def with_di(user: HTTPBasicCredentials = Depends(di_bearer)):

    return {"username" : user.username if user else None}

the second handler does inject the bearer itself and not the the bearer's __call__ method provides

This makes partially sense for me, but I'm still wondering if there is a way to get this to work

This is the failing test
https://github.com/mxab/fastapi-di-depends-issue/blob/main/tests/test_fastapi_di_depends_issue.py#L31

[mxab]

As a workarround I can use it like this:

@inject
async def workarround(
    request: Request, di_bearer=Provide[Container.bearer]
) -> HTTPBasicCredentials:

    return await di_bearer(request)


@app.get("/with_di_workarround")
def with_di_workarround(user: HTTPBasicCredentials = Depends(workarround)):

    return {"username": user.username if user else None}

But it's not pretty :)

[mxab]

As long as I don't type the di_bearer in the signature, otherwise FastAPI goes mad :)

async def workarround(
    request: Request, di_bearer:HttpBasic=Provide[Container.bearer]): ... # di_bearer:HttpBasic -> boom

[mxab]

ok the problem with the workarround is also that it breaks the open api endpoin :/

def test_openapi(client: TestClient):

    resp = client.get("/openapi.json")
    resp.raise_for_status()
    assert resp.status_code == 200

results in error:

TypeError: Object of type 'Provide' is not JSON serializable

[mxab]

ok forgot the Depends

@inject
async def workarround(
    request: Request, di_bearer: HTTPBasic = Depends(Provide[Container.bearer])
) -> HTTPBasicCredentials:

    return await di_bearer(request)

[mxab]

So the only question left is if there is a nice way as the workarround function ?

[adriangb]

I think part of the trouble stems from the fact that Depends looks for an instance of Security at compile time, before anything is injected. I believe it would get an instance of whatever Provide[Container.bearer] returns, which is not going to be an instance of fastapi.security.base.SecurityBase.